May 25, 2012 -- Drinking a daily glass of red wine not only tastes good to many people, but it's also good for the bacteria lining your large intestine.

A new Spanish study suggests that sipping about 9 ounces of Merlot or a low-alcohol red wine changed the mix of good and bad bacteria typically found in the colon in ways that can benefit your health.

Bacteria may sound like a bad thing to have in your intestinal tract, but having a balanced mix of them actually helps to digest food, regulate immune function, and produce vitamin K (which plays a key role in helping the blood clot).

Since the study results showed that Merlot and low-alcohol red wine had similar positive effects on intestinal bacteria, researchers suspect it's not due to the alcohol but to the polyphenol compounds found in the wine.

Polyphenols are helpful plant-based compounds found in a variety of foods and beverages. Besides red grapes, many other fruits and vegetables are rich sources of polyphenols, as are coffee, tea, chocolate, and some nuts.

Previous research has looked at whether polyphenols in the diet can influence the balance of intestinal bacteria. This study sought to explore whether drinking red wine can have a similar prebiotic effect. Prebiotics are substances you eat that help promote the growth of good gut bacteria.

Red, Red Wine

In this small study, which appears in the American Journal of Clinical Nutrition, researchers followed 10 healthy middle-aged men. For the first 15 days of the study, the men had no wine or other alcohol. This was followed by three 20-day periods in which the men were given one of three beverages to drink each day: They received either 9 ounces of Merlot, 9 ounces of low-alcohol-content red wine, or about 3 ounces of gin.

Unlike the red wines, gin contains no polyphenols, so it served as a comparison.

Throughout the study, volunteers were asked not to change their diets or
exercise habits. They were also told not to drink any additional alcohol. Blood, urine, and stool samples were collected from each man during all four study periods. And their weights and blood pressures were monitored.

The findings showed that the balance of intestinal bacteria shifted in the men in a similar way whether they drank the Merlot or low-alcohol red wine. In both cases, they had a larger percent of certain beneficial gut bacteria.

After drinking the polyphenol-rich beverages, the men also had lower blood pressure. It also decreased triglyceride levels, HDL cholesterol (the so-called good cholesterol), and C-reactive protein (CRP) levels, a measure of inflammation.

"This study was the first to show that regular, moderate consumption of red wine could have a noteworthy effect on the growth of select gut microbiota," the researchers conclude.